Dry friction clutches are often utilized to allow for selective engagement of an engine with an input shaft of a transmission. Many dry clutches have a bracket (sometimes referred to as a cover) that is spaced from and connected with an engine flywheel. Inside the bracket is a pressure plate that is torsionally connected to the bracket and is axially moveable towards the flywheel. Positioned between pressure plate and flywheel is a friction disc. The friction disc is torsionally connected with an input shaft of a transmission. To urge the pressure plate towards the flywheel to capture the friction disc with the flywheel, there is an apply spring or spring loaded lever. As the friction lining of the friction disc wears, adjustment is required. To provide for adjustment, many clutches have a multiple cam ring adjuster between the apply spring or lever and the pressure plate. Many of the adjuster arrangements have a first cam ring that is non-rotative that engages a second rotative ring. A torsional spring is provided to urge the second cam ring to rotate with respect to the first cam ring. As the second cam ring rotates, the distance between the apply spring or lever and an extreme end of the pressure plate increases to compensate for the friction plate wear.
Examples of dry friction clutches with cam ring adjustment mechanisms can be found by a review of U.S. Pat. Nos. 5,964,429 and 6,109,412 and 6,296,099. It is also desirable in dry friction clutches with adjustment mechanisms to limit the maximum amount of adjustment.
Although an adjustment mechanism is provided to prevent over-adjustment of the pressure plate, it is desirable to provide a hard fail-safe stop to prevent the pressure plate from axially coming too close to the flywheel. The bracket is U-shaped like a bowl with a central opening. The bowl shaped bracket has a main body or base that extends radially outward from the central opening. The bracket main body is axially spaced away from the engine flywheel. The bracket main body is joined with a generally axially extending tubular shaped side wall. An extreme end edge of the side wall fits into a circular rim of the flywheel. The fit of the bracket side wall into the pilot rim of the flywheel should be as snug as possible. Accordingly, the bracket side walls have an outer bevel to pilot the assembly of the bracket into the pilot rim of the engine flywheel. Proper concentric alignment of the bracket to the flywheel is important to ensure the clutch is centered to the flywheel and to reduce imbalance in applications that can cause excessive vehicle vibration. Proper concentric alignment also reduces wear of the clutch actuation components that can occur due to excessive relative movement from misalignment. Also, if interference between the bracket sidewall and the flywheel pilot rim occurs, results can be that the clutch will have an increased required force for installation potentially raising burrs in the clutch OD from the flywheel pilot rim. The burrs can make the clamping force of the mounting bolts to be so high due to interference that the clutch is unable to be installed.
The inside of the bracket is torsionally connected to the pressure plate by a series of geometrically spaced spring straps. The spring straps have one end pivotably connected with the pressure plate along an outer periphery of the pressure plate. An opposite end of the spring straps is pivotally connected along the inner side of the bracket main body by rivets. To allow for installation of the rivets of the spring straps that connects the pressure plate with the brackets, the bracket side walls have cut outs to allow for tooling access.
It is desirable to positively limit the distance that the pressure plate can move toward the fly wheel to prevent damage to the flywheel from rivets in over worn friction discs. Prior to the current invention, two main methods were used to provide the positive stop. One method was to connect the pressure plate to the main body of the bracket by extending bolts which acted like guide rails with a stop at the end. This method worked, but the force exerted on the bolts by the pressure plate (by virtue of the clutch actuating spring(s) caused the bracket axially extending side walls to warp, especially in the area adjacent to the cut outs provided for tooling access. Another method to limit axial movement of the pressure plate with respect to the bracket is to provide an outer radial rim (similar to that of a brim on a hat) connected to the side wall of the bracket. A lug is then provided on the pressure plate which radially extends outside of the tooling access cut out. The pressure plate lug has a bend to then be seated against the bracket outer radial rim. This design also causes unfavorable warping of the side wall since the portion of the sidewall closest to the tooling access cut out is structurally weakest portion of the bracket sidewall.
It is desirable to provide a positive stop for delivering axial traveled the pressure plate with respect to the bracket which provides less deformation in the geometry of the bracket side walls when the pressure plate is fully loading a stop that prevents axial travel of the pressure plate with respect to the bracket.